Ever since I bought her, she's always had a nasty hollow sound, increases with revs. When cold, she was really noisy, only after a minute or so running, would she quieten down. I put her on the ramp last Monday, and discovered 2 things: The offside flexi joint was blowing badly, cracked almost all round, held together mostly by the braid. The offside catalyst had a welded "trapdoor", meaning one thing - it had been cut open, and gutted, hence the resonance. Got a catalyst, brand new, but for a Honda 2,0 16V V-tech unit for £40. Not worth going for the Sport catalyst system, and full custom stainless exhaust, as it'll need to be modified again, to suit the S8 motor. Modified it by cutting off the flanges both end, and welding pipework on to suit the Audi set-up, and fitted it yesterday. It was blowing from the front joint, so I re-sealed it today, with a couple of new 58mm clamps, and boy, does she sound good! I'll try putting up some sound clips later on.